Fuel injectors, such as those used in Diesel engines require a high pressure to inject fuel into a combustion chamber of the engine. One method of pressurizing the fuel is to use a high pressure hydraulic fluid to pressurize the fuel prior to injecting the fuel into the combustion chamber. One such hydraulic fluid commonly used is an engine oil which also serves to lubricate and cool various engine components, such as pistons and valves. A drawback to using the engine oil is that the oil may become contaminated with combustion by-products making the oil both corrosive and abrasive to hydraulic components.
Additionally, modern fuel injectors require that fuel be delivered at various pressures depending on rapidly changing operating conditions of the engine. In particular, fuel pressure requirements may be varied as a result of changing engine speed, temperature, and engine load. To accommodate these changes, a pressure control valve must be used which can rapidly vary the pressure of the engine oil used to pressurize the fuel in response to the changing engine operating conditions. When the pressure control valve is exposed to the corrosive and abrasive engine oil, it is possible that the valve will wear and be unable to supply the pressurized engine oil as precisely as required. A drawback to this loss of precise pressure control is that the engine may operate at less than its"" optimal operating point for a particular set of operating conditions.
What is needed therefore is a pressure control valve having enhanced durability which overcomes the above-mentioned drawbacks.
In accordance with a first embodiment of the present invention, there is provided a pressure control valve having a cage with an inlet and an outlet in fluid communication with an engine oil circuit. The pressure control valve further has a spool in sliding engagement within the cage which blocks fluid communication between the inlet and the outlet when the spool is in the first position and places the inlet in fluid communication with the outlet when the spool is in the second position. A thin film coating is applied to an outer surface of the spool. The pressure control valve yet further has an actuator which controls movement of the spool from the first position to the second position. The coating reduces wear on the outer surface of the spool due to exposure of the spool to the engine oil and sliding engagement with the cage.
In accordance with a second embodiment of the present invention, there is provided a component in a hydraulic system of an engine. The component includes a low alloy steel substrate and a coating on said low alloy steel substrate. The coating is selected from the group consisting of chromium nitride, zirconium nitride, molybdenum nitride, titanium-carbon-nitride, or zirconium-carbon-nitride. The said component is adapted to be exposed to a fluid within said fuel injection system and said component is further moveable within said fuel injection system relative to an adjacent component within said fuel injection system.